Under operating nuclear reactor, fluid vibrations result from the coolant circulation with a pump and vapor generation in a core, etc. By this fluid vibration, vivlation fatigue will be continuously accumulated in the internal structure of the nuclear reactor. For this reason, it is required to carry out real time measurement of the vibration state of the internal structure under the nuclear reactor operating.
However, it is technically difficult measuring a vibration of the internal structure directly, thus it is required providing a device outside of the nuclear reactor for indirect measurement.
It is generally using an ultrasonic method for measuring vibration of object inside container indirectly from outside container (for example, document; Japanese Patent Application Laid-Open No. 2009-229355).
By the way, above document describes measurement of the internal structure vibration using an ultrasonic sensor, but it is not indicated about installing method of an ultrasonic sensor on the surface of a pressure vessel.
Generally, the surface of a pressure vessel is exposed to high temperature and high radiation. The ultrasonic sensor is exposed under such severe environment for a long time. Moreover, it is very narrow space between the pressure vessel and the reactor container. For this reason, it is desired easy install in that narrow space, and also without interfere other work when installing an ultrasonic sensor on a surface of pressure vessel.
Present embodiments were made in consideration of such a situation, and aim at providing the vibration measurement technology for nuclear reactor internal structure, the ultrasonic sensor being easy installation for narrow space, and acting on the surface of a pressure vessel under severe environment for a long time.